The present invention relates to a retainer connecting a fused stem and a lamp capsule in a lamp assembly.
Currently, various techniques are being used or are being investigated for manufacturing Halogen type lamps. A first method incorporates a double-ended halogen capsule into a non-standard incandescent envelope. This method has a disadvantage in being restricted to a non-standard envelope and can not be used in “conventional” lighting envelopes known to those of ordinary skill in the art. However, the non-standard envelope is costly. In addition, the outer glass envelope is subject to breakage, which may present a fire hazard as the wall temperature of the capsule is high enough to ignite various materials, such as paper and fabric.
Another known capsule uses a relatively thick, heavy glass walled envelope to minimize possible breakage. Such a heavy glass walled envelope is also non-standard and expensive to manufacture. In addition, the heavy glass walled envelope reduces the transmission of light and while the heavy glass walled envelope reduces the risk of breakage, when breakage does occur, the fire hazard is still present and a user is still subject to burns caused by exposure to the hot capsule.
A number of designs have been offered to interrupt electrical current to an inner lamp and reduce or effectively eliminate the fire hazard in the event of damage to an outer lamp envelope. A method known for use with a high intensity discharge lamp involves positioning an oxidizable fuse within the outer envelope of the lamp and in series with the lamp circuit. Such a fuse oxidizes and interrupts the lamp circuit, in the event the outer envelope breaks and exposes the fuse to air, thereby extinguishing the lamp and reducing the risk of fire.
One of the concerns in manufacturing such lamps is providing a satisfactory manner in which to support the lamp capsule and fuse within the outer envelope. It is known to fabricate such lamps by electrically and mechanically connecting the fuse directly to electrical conductors within the outer envelope by welding and the like. This may involve a complicated fabrication procedure, and in some instances it may be difficult to accurately maintain the repeatability and failure parameters of the fuse. When using a coiled fuse, for example, the pitch of the coil determines the repeatability and failure parameters of the fuse. Specifically, the length of the fuse defined as from the start of the coiled part of the fuse to the end of the coiled part of the fuse should be maintained at a constant length (±0.05 mm). In addition, the lamp capsule must be adequately supported within the outer envelope. Such supports may be complicated and may typically include straps, which surround the capsule at opposite ends thereof and are attached to One or more support rods extending from an inlead protruding from the lamp stem.
An example of a high intensity discharge lamp, which includes an oxidizable fuse within the outer envelope, is described in U.S. Pat. No. 4,361,782. In this patent, the inner lamp capsule is supported within an outer lamp envelope by strap clips welded to a rod, which is welded to an inlead extending from the lamp stem, the rod extending to a looped clip which engages an anchoring dimple of the outer envelope. The oxidizable fuse is part of the lamp circuit being connected to an inlead and a main electrode. However, the rod to which the fuse is connected is subject to bending. Such bending would bring the fuse outside the above-noted acceptable length tolerance.
A further improvement is shown in U.S. Pat. No. 5,023,505 to Ratliff et al. in which FIGS. 1 to 3 depict an electric lamp 2 in a hermetically sealed outer glass envelope 4. A pair of electrical conductors 8 and 10 is sealed into and passes through the stem 12 of the outer glass envelope in a conventional manner. An arc tube 14 having a pair of spaced electrodes 16 and 18 is electrically connected to a respective electrical conductor in a conventional manner to provide an electrical circuit.
A support member 22 supports arc tube 14 and is electrically isolated from the electrical circuit and is within the outer glass envelope 4. The support member 22 is held in place relative to the stem 12 at one end of the support member by a stem clip 24. The support member can alternatively be welded on the outer surface of the stem clip. As seen in FIG. 2, the support member includes two elongated legs 38 and 40, which are preferably welded to the stem clip 24.
As further seen in FIG. 2, the support member 22 also supports a conventional heat shield 42 by first strap member 44 and second strap member 46. The first and second strap members 44 and 46 are welded to legs 38 and 40 so as to extend therebetween in a direction normal to the longitudinal axis 36.
As depicted in FIG. 3, each elongated leg 38 and 40 is disposed between an inner surface 52 of the stem clip 24 and outer surface 54 of an inert material 50 so that the stem clip 24 forms a sleeve. The sleeve-like stem clip 24 includes a first end 56 and an opposite second end 58. In assembling the stem clip 24, inert material 50 is wrapped around the stem 12, and the stem clip 24 is firmly wrapped around stem 12 with the sleeve-like inert material 50 interposed between the inner surface 52 of the stem clip and the outer surface of the stem 12. Upon completion of the wrapping of the stem clip 24, the ends 56 and 58 are welded together at 60.
As depicted in FIGS. 1 and 2, an oxidizable fuse 48 may be included outside of the arc tube 14 and within the outer envelope 4. Fuse 48 interrupts the lamp current in the event the outer envelope is fractured in order to prevent possible exposure to ultraviolet light.
However, the design of Ratliff et al. has a number of problems. First, the support member of FIGS. 1 to 3 requires various welds to connect the legs 38, 40 to the stem clip 24 and to straps 44, 46. The legs require support at the stem clip 24, the straps 44, 46 and the top of the support near 48. Accordingly, the support shown in FIGS. 1–3 is still fairly complicated and unwieldy. Second, the fuse 48 is relatively long and subject to damage during manufacturing. Specifically, the fuse may contact legs 38, 40 during insertion into the envelope 4 causing the fuse to break or causing the fuse to short. Further since the legs 38, 40 are spindly, the support member 22 is subject to bending or twisting which would place stresses on the fuse causing the fuse to break and render the lamp inoperable. In addition, since the fuse 48 may be a coiled construct, such bending would affect the length of the coiled section and bring the fuse outside acceptable tolerances.
In attempts to overcome the problems of the conventional electric lamp and simplify the support, other lamps have been offered. Another conventional electric lamp such as that taught by U.S. 2003/0057834 to Kling and shown in FIGS. 4 and 5 illustrate a support 100 assembled with a lamp 101. Support 100 includes a first portion 102 mechanically connectable to a lamp capsule 103. A conductive second portion 104 of the support 100 is electrically and mechanically connectable to a first lead wire 105, as for example, by welding. The support 100 also includes a conductive third portion 106 electrically and mechanically connected to a first electrical conductor 107. A fuse 109 is electrically and mechanically connected between the second portion 104 and the third portion 106. A second electrical conductor 111 is electrically connected to a second lead wire 113. In FIGS. 4 and 5, the fuse 109 is connected to the second portion 104 and third portion 106 by clamps 108 and 110, respectively.
The support 100 for the fuse is attached to lamp capsule 103, such that the first portion 102 of the support is mechanically connected to the lamp capsule 103. Walls 114 and 116 of the lamp capsule 103, including flanges 120 and 122, are structured and arranged to slidingly mate with rail 124 or rail 132 of the lamp capsule 103. Rail 124 is dimensioned to be force fit into the opening 126 between the walls 114 and 116 of the support 100, the walls 114, 116 bearing against respective rail surfaces to hold the lamp capsule 103 in place relative to the support 100. The lamp capsule 103 may have one or more locking segments that engage respective mating locking segments of the support walls to hold the capsule in place relative to the support.
The second portion 104 of the support 100 comprises a first segment 142 extending from the third portion 106, and a second segment 144 extending from the first segment 142. The lead wire 105 is electrically and mechanically connected to the second segment 144, as for example, by welding the lead wire to surface 146.
The support of KLING also has various problems. Specifically, there are automation difficulties because the heavy leads require non-standard glass forming techniques and can be prone to press failures in the lead entry area. Additionally, the step of separating the clip “bridge” from the fuse clamp creates problems in maintaining the tolerance requirements of the fuse length. Specifically, maintaining the centerline distance between clamps 108, 110 is critical. When the “bridge” is separated, stored energy is released in the relevant parts. Accordingly, when a segment of the retainer (106′ in FIG. 5) is removed by the cutting process, the release of stored energy allows movement of the retainer changing the centerline distance and subsequently leading to loss of tolerance in the fuse length.